RF64 datasheet(15/76 Pages) ETC2

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RF64

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With the recommended Bill Of Materials (BOM) of the reference design of section 7.5.3, the PLL prototype is the

following:



64 ≤ R ≤ 169

 S < P+1

 LLBW = 15 kHz nominal

 Startup times and reference frequency spurs as specified.

3.2.5. Voltage Controlled Oscillator

The integrated VCO requires only two external tank circuit inductors. As the input is differential, the two inductors

should have the same nominal value. The performance of these components is important for both the phase noise

and the power consumption of the PLL. It is recommended that a pair of high Q factor inductors is selected. These

should be mounted orthogonally to other inductors (in particular the PA choke) to reduce spurious coupling

between the PA and VCO. In addition, such measures may reduce radiated pulling effects and undesirable

transient behavior, thus minimizing spectral occupancy. Note that ensuring a symmetrical layout of the VCO

inductors will further improve PLL spectral purity.

For best performance wound type inductors, with tight tolerance, should be used as described in section 7.5.3.

3.2.5.1. SW Settings of the VCO

To guarantee the optimum operation of the VCO over the RF64

‟s frequency and temperature ranges, the

following settings should be programmed into the RF64:

Target channel

(MHz)

300-

330

320-

350

350-

390

390-

430

430-

470

470-

510

Freq_band

000

001

010

011

100

101

Table 10: MCParam_Freq_band Setting

3.2.5.2. Trimming the VCO Tank by Hardware and Software

To ensure that the frequency band of operation may be accurately addressed by the R, P and S dividers of the

synthesizer, it is necessary to ensure that the VCO is correctly centered. Note that for the reference design (see

section 7.5) no centering is necessary. However, any deviation from the reference design may require the

optimization procedure, outlined below, to be implemented. This procedure is simplified thanks to the built-in VCO

trimming feature which is controlled over the SPI interface. This tuning does not require any RF test equipment,

and can be achieved by simply measuring Vtune, the voltage between pins 6 (LFM) and 7 (LFP).

The VCO is centered if the voltage is within the range:

100 ≤ Vtune(mV ) ≤ 200

Note that this measurement should be conducted when in transmit mode at the center frequency of the desired

band (for example ~315 MHz in the 300-330 MHz band), with the appropriate MCParam_Freq_band setting.

If this inequality is not satisfied then adjust the MCParam_VCO_trim bits from 00 whilst monitoring Vtune. This

allows the VCO voltage to be trimmed in + 60 mV increments. Should the desired voltage range be inaccessible,

the voltage may be adjusted further by changing the tank circuit inductance value. Note that an increase in

inductance will result in an increase Vtune.

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